This invention relates to improvements in axial piston pumps or motors and comprises means for controlling the clearance between the port-face and the rotating barrel of such pumps or motors (hereinafter referred to as pumps).
In axial piston hydraulic pumps, where distribution of the working fluid to and from the working cylinders carried by a rotating barrel is effected by co-operating port-faces on the barrel and on the casing, it is usual to employ minimal porting at minimal operating radius to minimize face leakage and, more importantly, port-face fluid-shear drag and heating which can become critical at low through-put and low pressure-leakage. Also, of course, the effective port-face areas have to balance the combined piston areas, as under-balance would allow rubbing contact and wear, whilst over-balance increases leakage and therefore volumetric efficiency loss. Further, there is a substantial imbalance variation as the cylinder ports successively come into and out of communication with the delivery port of the casing port-face.